Chitosan, a natural polysaccharide, is commercially important because of its properties as a natural polycationic polymer which is soluble in dilute acid. It has many uses as a flocculant or precipitation agent and is also used as a cross linkable matrix for immobilization of enzymes or microbial cells. Many other uses are suggested from its film forming properties and its polyelectrolyte behavior. Chitin, the precursor of chitosan is available, for example, in the shells of crustaceans from which it can be isolated after extracting the shells with acid and alkali to remove mineral matter and protein components.
The byproducts of fermentation processes such as the biomass recovered after the controlled fermentation of fungi, molds and yeasts contain chitin together with other biopolymers such as glucan. Muzzarelli discloses in German Patent Publication DE-05 No. 2,923,802 a method for obtaining a chitosan-glucan complex by treating the mycelia of hyphomycetes such as those from the genus Aspergillus with a strong, concentrated alkali at a temperature near the boiling point of the solution to solubilize the mycelial material other than a resulting chitosan-glucan complex and then recovering this insoluble material. This patent discloses a typical procedure in which the biomass is treated with a 30-50% sodium hydroxide solution at its boiling temperature (118.degree.-130.degree. C.) for 4-6 hours. The author states that at a lower temperature, shorter times of treatment and lower sodium hydroxide concentrations, glucan is solubilized and removed less effectively and there is only limited deacetylation of the chitin to form chitosan. This would be inimical to his stated goal of forming a chitosan-glucan complex which is capable of collecting and binding manganese ions.
Muzzarelli, Tanfani and Scarpini report in Biotechnology and Bioengineering, Vol. XXII, pp. 885-896 (1980) that waste mycelia of Aspergillus niger from citric acid production can be treated with boiling 30-40% NaOH aqueous solutions for 4-6 hours to obtain an insoluble chitosan-glucan complex.